diff --git a/vdirsyncer/cli.py b/vdirsyncer/cli.py
index 1d17117..abe5cb2 100644
--- a/vdirsyncer/cli.py
+++ b/vdirsyncer/cli.py
@@ -14,10 +14,9 @@ import sys
 import argvard
 
 from .storage import storage_names
-from .sync import sync
+from .sync import sync, StorageEmpty
 from .utils import expand_path, parse_options, split_dict
 
-import vdirsyncer.exceptions as exceptions
 import vdirsyncer.log as log
 
 
@@ -312,7 +311,7 @@ def sync_collection(config_a, config_b, pair_name, collection, pair_options,
             conflict_resolution=pair_options.get('conflict_resolution', None),
             force_delete=status_name in force_delete
         )
-    except exceptions.StorageEmpty as e:
+    except StorageEmpty as e:
         side = 'a' if e.empty_storage is a else 'b'
         storage = e.empty_storage
         raise CliError(
diff --git a/vdirsyncer/storage/http.py b/vdirsyncer/storage/http.py
index 5f05736..396994e 100644
--- a/vdirsyncer/storage/http.py
+++ b/vdirsyncer/storage/http.py
@@ -153,8 +153,9 @@ class HttpStorage(Storage):
         self._items.clear()
         for i, item in enumerate(split_collection(r.text.splitlines())):
             item = Item(u'\n'.join(item), needs_uid=False)
-            uid = item.uid if item.uid is not None else i
-            self._items[uid] = item
+            if item.uid is None:
+                item.uid = i
+            self._items[item.uid] = item
 
         for uid, item in self._items.items():
             yield uid, hashlib.sha256(item.raw.encode('utf-8')).hexdigest()